Versatile Dye Laser Generator-Amplifier System for Intense Tunable Picosecond Pulse Generation

Abstract. Passively mode-locked ruby-laser pulses are used to generate nearly diffraction-limited picosecond light pulses in a dye cell by longitudinally amplified spontaneous emission. The output pulses are amplified in three longitudinally pumped dye cells, then spectrally filtered with a grating spectrometer and finally reamplified in a fourth dye amplifier in order to generate intense frequency tunable picosecond light pulses. PACS: 42.55M, 42.60 Various pulsed dye laser systems are available for tunable picosecond pulse generation [1, 2]. Flash-lamp pumped mode-locked dye lasers [3], synchron-ously pumped lasers [4], short-cavity resonators [5], quenched transient lasers [6], distributed feedback lasers [7], and amplified spontaneous emission sys-tems [8] have been investigated. The arrangements applying amplified spontaneous emission (ASE) may be grouped into longitudinall

Community Food Initiatives: Grassroots Innovation in Practice

As community food initiatives have become more widespread and well-established, they have become increasingly recognised for their ability to generate innovative civil society responses to a range of local needs and societal challenges (not least those framed around sustainability and social justice). However, despite their potential for catalysing action at the grassroots, significant challenges are faced in overcoming limited resources and power; and in attempting to maintain internal stability whilst working towards generating long-term and transformative social change. This thesis advances understanding of the dynamics of grassroots innovation by examining how community food initiatives negotiate the landscape of opportunities and challenges they face, in order to work towards developing sustainable practices at the local level in line with societal-level aims and objectives. The thesis critically engages a communities of practice approach, drawing on understanding of social learning to develop a framework for analysing innovation as both negotiated within communities, and co-produced through connections as part of landscapes of practice. In-depth engagement with collaborative partners Grow Sheffield and Feeding Manchester and their broader networks, has enabled analysis at a range of scales, exploring the role that shared histories of learning and connections across the landscape play in the development of grassroots innovation. In the context of increasing resource scarcity, the thesis finds that the interconnected challenges of maintaining survival and creating long-term impact are central to framing of innovation and learning. Capacity for innovation is not confined to organisations, but is carried within and between communities of practice and is generated through interaction across the landscape. In the final stages of the research, findings were put into practice by bringing together key partners to facilitate shared learning between cities and catalyse practical action towards developing a stronger network of community food initiatives in Sheffield. By developing understanding of the dynamics of grassroots innovation, the findings of this thesis contribute to debates around the role that community based organisations can play in transitions to sustainability. The thesis argues against focus on outcomes, scaling up, diffusion, and narrow understandings of knowledge for sustainability; and challenges a binary view of internal versus external processes. Instead, it demonstrates the value of understanding community organisations as generators of capacity for innovation, co-producing sustainable practices as they work across boundaries in landscapes of practice

Multi-wavelength, all-solid-state, continuous wave mode locked picosecond Raman laser

We demonstrate the operation of a cascaded continuous wave (CW) mode-locked Raman oscillator. The output pulses were compressed from 28 ps at 532 nm down to 6.5 ps at 559 nm (first Stokes) and 5.5 ps at 589 nm (second Stokes). The maximum output was 2.5 W at 559 nm and 1.4 W at 589 nm with slope efficiencies up to 52%. This technique allows simple and efficient generation of short-pulse radiation to the cascaded Stokes wavelengths, extending the mode-locked operation of Raman lasers to a wider range of visible wavelengths between 500 - 650 nm based on standard inexpensive picosecond Nd:YAG oscillators

Prostate Cancer Nodal Staging: Using Deep Learning to Predict 68Ga-PSMA-Positivity from CT Imaging Alone

Lymphatic spread determines treatment decisions in prostate cancer (PCa) patients. 68Ga-PSMA-PET/CT can be performed, although cost remains high and availability is limited. Therefore, computed tomography (CT) continues to be the most used modality for PCa staging. We assessed if convolutional neural networks (CNNs) can be trained to determine 68Ga-PSMA-PET/CT-lymph node status from CT alone. In 549 patients with 68Ga-PSMA PET/CT imaging, 2616 lymph nodes were segmented. Using PET as a reference standard, three CNNs were trained. Training sets balanced for infiltration status, lymph node location and additionally, masked images, were used for training. CNNs were evaluated using a separate test set and performance was compared to radiologists' assessments and random forest classifiers. Heatmaps maps were used to identify the performance determining image regions. The CNNs performed with an Area-Under-the-Curve of 0.95 (status balanced) and 0.86 (location balanced, masked), compared to an AUC of 0.81 of experienced radiologists. Interestingly, CNNs used anatomical surroundings to increase their performance, "learning" the infiltration probabilities of anatomical locations. In conclusion, CNNs have the potential to build a well performing CT-based biomarker for lymph node metastases in PCa, with different types of class balancing strongly affecting CNN performance

Coil excited pseudo direct drive electrical machines

A Pseudo Direct Drive (PDD) equipped with a coil excited high-speed (HS) rotor is presented. An analytical model which predicts the flux density in the air spaces and permanent magnets (PM) of the PDD is presented, and it is shown, that a good agreement exists between the analytical and finite element (FE) predictions. Furthermore, the model is employed to investigate the effects of the key design parameters on the performance of a coil excited PDD for a 10MW wind turbine application and an optimised design is proposed. It is shown that shear stress in excess of 100kPa can be achieved, and that compared to a PM excited PDD a reduction in PM mass can be realized. It is also shown that the efficiency over the operating range of the wind turbine can be maximized by adopting an appropriate control strategy of the HS rotor excitation currents